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Equine veterinary journal2026; doi: 10.1002/evj.70157

Tracheal wash culture is not associated with bronchial infection, remodelling or inflammation in horses with asthma.

Abstract: Antimicrobials are commonly prescribed for the treatment of equine asthma, despite limited evidence supporting their use. Tracheal wash (TW) bacterial culture results are known to influence antimicrobial prescription decisions. Objective: To determine whether a positive TW bacterial culture in horses with asthma is associated with bronchial infection or colonisation, increased bronchial remodelling and airway inflammation by evaluating the presence of bacteria and airway remodelling in endobronchial biopsies, as well as bronchoalveolar lavage fluid (BALF) cytology and tracheal mucus scores. Methods: Retrospective blinded case-control study. Methods: Tracheal wash aerobic bacterial culture, endobronchial biopsies, BALF cytology and tracheal mucus scores from horses with severe equine asthma (SEA) (n = 13), mild-to-moderate equine asthma (MEA) (n = 9) and control horses (n = 9) were evaluated. Results: Tracheal wash cultures were positive in 8/13 horses with SEA, 6/9 horses with MEA and 8/9 control horses. No bacteria were identified on Gram stains in any endobronchial biopsy samples. Semiquantitative histologic scores from endobronchial biopsies did not differ significantly between asthmatic horses with positive versus negative TW cultures (p = 0.4). Neutrophil percentages in BALF were not significantly different between asthmatic horses with a positive and negative TW culture (p = 0.5). Tracheal mucus scores did not differ between asthmatic horses with positive versus negative TW cultures (p = 0.7). Conclusions: Small sample size, absence of endobronchial biopsies with bacterial presence. Conclusions: A positive bacterial TW culture in horses with asthma is not associated with bronchial infection, bacterial colonisation, increased bronchial remodelling or increased airway inflammation. Therefore, a positive TW culture in these cases does not confirm the presence of a secondary bacterial infection. Tracheal wash culture results alone should not be considered a primary determinant when making treatment decisions for equine asthma.
© 2026 The Author(s). Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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Publication Date: 2026-03-17 PubMed ID: 41844169DOI: 10.1002/evj.70157Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study investigated whether a positive bacterial culture from a tracheal wash (TW) in horses with asthma indicates true bronchial infection, airway remodeling, or inflammation.
  • Findings showed that positive TW cultures do not correlate with bronchial infection or worsening asthma features, suggesting antimicrobial treatment based solely on TW culture results may be unwarranted.

Background and Objective

  • Antimicrobials are frequently prescribed for equine asthma despite limited evidence supporting their efficacy in this context.
  • Veterinarians often rely on bacterial culture results from tracheal wash samples to decide on antimicrobial use.
  • The study aimed to determine if positive bacterial cultures from TW samples in asthmatic horses are linked to:
    • Actual bronchial infection or bacterial colonization
    • Increased bronchial remodeling (structural changes in the airway)
    • Elevated airway inflammation
  • Evaluations included: analyzing endobronchial biopsy samples for bacteria and remodeling, bronchoalveolar lavage fluid (BALF) cytology for inflammation, and scoring tracheal mucus.

Methods

  • The study was a retrospective, blinded case-control design.
  • Sample groups included:
    • 13 horses with severe equine asthma (SEA)
    • 9 horses with mild-to-moderate equine asthma (MEA)
    • 9 control horses without asthma
  • For all horses, researchers collected and analyzed:
    • Tracheal wash aerobic bacterial cultures
    • Endobronchial biopsies for histological analysis and bacterial presence using Gram stains
    • Bronchoalveolar lavage fluid (BALF) cytology to measure neutrophil percentages as inflammation markers
    • Tracheal mucus scoring to assess mucus accumulation

Results

  • Positive TW bacterial cultures were found in:
    • 8 out of 13 SEA horses
    • 6 out of 9 MEA horses
    • 8 out of 9 control horses
  • No bacteria were detected in any endobronchial biopsy specimens when using Gram stains.
  • Histologic scores assessing bronchial remodeling did not significantly differ between asthmatic horses with positive versus negative TW cultures (p=0.4).
  • Neutrophil percentages in BALF, indicating airway inflammation, also showed no significant difference between horses with positive and negative TW cultures (p=0.5).
  • Tracheal mucus scores were similar regardless of TW culture results (p=0.7).

Conclusions

  • Positive bacterial cultures from tracheal washes in horses with asthma do not equate to clear evidence of bronchial infection or colonization.
  • There is no associated increase in bronchial remodeling or airway inflammation linked to positive TW cultures.
  • The study emphasizes that TW culture results alone are insufficient to confirm secondary bacterial infections in asthmatic horses.
  • Consequently, veterinarians should avoid basing antimicrobial treatment decisions solely on TW culture results in equine asthma cases.
  • The study acknowledged limitations such as a small sample size and the absence of bacterial detection in biopsy samples, which may influence generalizability.

Significance and Implications

  • This research challenges the common practice of prescribing antimicrobials for equine asthma based purely on positive TW bacterial culture findings.
  • It promotes more judicious use of antimicrobials, potentially reducing unnecessary antibiotic exposure and the risk of antimicrobial resistance.
  • Future studies with larger sample sizes and advanced bacterial detection techniques could help validate these findings and influence clinical guidelines.

Cite This Article

APA
Leduc L, St-Jean G, Lavoie JP. (2026). Tracheal wash culture is not associated with bronchial infection, remodelling or inflammation in horses with asthma. Equine Vet J. https://doi.org/10.1002/evj.70157

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English

Researcher Affiliations

Leduc, Laurence
  • Département des Sciences Cliniques, Faculté de médecine vétérinaire, Université de Montréal, Montreal, Canada.
St-Jean, Guillaume
  • Département de pathologie et microbiologie, Faculté de médecine vétérinaire, Université de Montréal, Montreal, Canada.
Lavoie, Jean-Pierre
  • Département des Sciences Cliniques, Faculté de médecine vétérinaire, Université de Montréal, Montreal, Canada.

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